|Isotelus rex is on the far right.|
Isotelus probably crawled along the sea floor and probably had to avoid predators like nautiloids. It was a kind of trilobite called an asaphid, which were trilobites that usually had between five and twelve segments in the thorax, and the pygidium and cephalon were similar in size.
The largest complete specimen of Isotelus rex was found in Manitoba, Canada in 1999. Isotelus maxiumus, another large species, has been found in Ohio.